With an entourage of 500 staff, an armour-plated limousine and a fleet of decoy helicopters, America's new president will arrive for his first visit to Britain amid huge razzmatazz on Tuesday for the G20 summit. But it will be his closed-door meetings with world leaders that are likely to prove the most significant of the trip

Britain will get its first chance to see Barack Obama this week when a White House cavalcade - complete with armoured limousines, helicopters, 200 US secret service staff and a six-doctor medical team - sweeps into the UK.

Obama will fly into London for his first visit to the UK as president of the United States on Tuesday to take part in the G20 summit in the capital's Docklands area. He will not be travelling light.

More than 500 officials and staff will accompany the president on his tour this week - along with a mass of high-tech security equipment, including the $300,000 presidential limousine, known as The Beast. Fitted with night-vision camera, reinforced steel plating, tear- gas cannon and oxygen tanks, the vehicle is the ultimate in heavy armoured transport.

In addition, a team from the White House kitchen will travel with the president to prepare his food. As one official put it: "When the president travels, the White House travels with him, right down to the car he drives, the water he drinks, the gasoline he uses, the food he eats. America is still the sole superpower and the president must have the ability to handle any crisis, anywhere, any time."

US security teams have already carried out three visits to prepare for Obama's first official visit to Britain. The first was a "site survey", the second a "pre-advance visit" which was carried out to pick sites that the president would visit. Finally there was the "advance trip", which took place last week. Its purpose was to set up equipment, sweep venues for electronic bugs, test food for poison and measure air quality for bacteria.

Obama will start his first presidential visit to Europe when he steps down from the US presidential jet, Air Force One, at Stansted airport on Tuesday. The Boeing 747-200B is fitted with its own gym, electronic defence units and shielding to protect its complex communication devices from radiation from nuclear blasts. Among the officials on the flight will be a military officer carrying America's nuclear missile launch codes.

Obama will then be flown to central London in a VH-3D helicopter known as Marine One. Again, high-tech security will dominate his journey. Marine One is fitted with flares that can be fired to confuse heat-seeking missiles and always flies in groups containing several identical decoy helicopters.

While in town, the president will be guarded by more than 200 US secret servicemen - easily identifiable by their shirt-cuff radios and Ray-Ban sunglasses. Obama has already had some time to get used their attention. It was decided 18 months ago, when he was still a presidential candidate, that his African-American background put him at particular risk of an assassination attempt and he was provided with his security guards.

And should anything befall the President, a White House medical unit will be at hand to provide emergency care. The team consists of surgeons, nurses and other medical personnel and carries supplies of blood of the type AB, the president's blood group. At the same time, Obama will be constantly minded by his personal aide Reggie Love, who dials his BlackBerry, fetches his jacket and tie and supplies him with snacks. First Lady Michelle Obama will also have a coterie of assistants, including a secretary, a press officer and several bodyguards.

It is a striking presence and shows that, for the next few days, London, not Washington, will be the beating heart of American foreign policy. At the end of the week Obama and his massive retinue will head off for meetings in France, Germany and the Czech Republic, although not before he has indulged in an unprecedented whirlwind of diplomatic activity - he and his advisers will not just be involved in complex summit negotiations, but will also be camped out in London conducting a series of individual high-level mini-summits with the most powerful leaders in the world.

Indeed, despite all the heat and fury over this week's G20, the most important work might actually emerge from the meetings that Obama and his team have scheduled on the side, far away from the debate over the economic crisis. In effect, if the G20 were a party with a guest list, then Obama's series of mini-summits would be a VIP room; open only to a select few powerful players and conducted firmly behind closed doors...